Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quantos acordos coletivos foram assinados pelo 'Sindicato Nacional dos Trabalhadores Hospitalares' entre 2015 e 2019?
 ###Tabelas: 
CREATE TABLE collective_bargaining_agreements (agreement_id INT, union_id INT, agreement_date DATE, agreement_status VARCHAR(255)); CREATE TABLE unions (union_id INT, union_name VARCHAR(255)); INSERT INTO unions (union_id, union_name) VALUES (123, 'United Workers Union'); INSERT INTO unions (union_id, union_name) VALUES (456, 'National Union of Hospital Workers'); INSERT INTO collective_bargaining_agreements (agreement_id, union_id, agreement_date, agreement_status) VALUES (1, 456, '2014-01-01', 'Signed'); INSERT INTO collective_bargaining_agreements (agreement_id, union_id, agreement_date, agreement_status) VALUES (2, 456, '2020-01-01', 'Drafted');
SELECT COUNT(*) FROM collective_bargaining_agreements c WHERE c.union_id = (SELECT u.union_id FROM unions u WHERE u.union_name = 'National Union of Hospital Workers') AND c.agreement_date BETWEEN '2015-01-01' AND '2019-12-31' AND c.agreement_status = 'Signed';